Coating method and apparatus for deposition of polymer-forming vapor under vacuum



p 1968 F. R. TlTTMANN ETAL 3,379,

COATING METHCD AND APPARATUS FOR DEPOSITION OF POLYMER-FORMING VAPORUNDER VACUUM Filed May 1964 5 Sheets-Sheet l INVENTORS FREDERICK R.TITTMANN WILLlAM M. JAYNE,JR.

ar%m

A T TORNEV Aprll 1968 F. R. TITTMANN ETAL 3,379,803

COATING METHOD AND APPARATUS FOR DEPOSITION OF POLYMER-FORMING VAPORUNDER VACUUM Filed May 4, 1964 3 Sheets-Sheet 2 lei/2% GE X I INVENTORSFREDERICK R. TITTMANN 0 g bx M Z6 WILLIAM M. JAYNE,JR.

L By 4. {A

ATTORNEY April 1968 FR. TITTMANN ETAL 3,379,

COATING METHOD AND APPARATUS FOR DEPOSITION OF POLYMERFORMING VAPORUNDER VACUUM Filed May 1964 5 Sheets-Sheet 5 INVENTORS FREDERICK R.TITTMANN WILLIAM M. JAYNE,JR.

A T TO/PNEY United States Patent 3,379,803 COATING METHOD AND APPARATUSFOR DEPO- SITION 0F POLYMER-FORMING VAPOR UNDER VACUUM Frederick R.Tittmann, Plainfield, and William M. Jayne, Jr., Basking Ridge, N.J.,assignors to Union Carbide Corporation, 'a corporation of New York FiledMay 4, 1964, Ser. No. 364,381 28 Claims. (Cl. 264-81) ABSTRACT OF THEDISCLOSURE A method and apparatus is provided for coating substratesurfaces with a polymer forming vapor. The substrate is coated in avapor deposition zone having terminal differential pressure gaseousseals. The deposition zone and substrate handling means are confinedWithin a housing adapted to provide a pressure envelope to aid inconfining polymer forming vapors to the deposition zone.

This invention relates to a method and apparatus for coating substratesurfaces with a polymer-forming vapor. More particularly, this inventionrelates to a coating method and apparatus for continuously orsemi-continuously coating metallic or non-metallic substrates of variouscross-sectional profiles with a continuous polymeric film formed byvapor deposition.

Recently, it has been found that extremely thin, yet continuous,polymeric film can be vapor deposited on a wide variety of substratesurfaces. Foremost, among such vapor-deposited polymers are the polymersof the pxylylene family. Poly-p-xylylenes are insoluble in every commonorganic solvent at room temperature and are tough, moisture resistantand exhibit low permeability to most gases and vapors. These polymershave been found to remain tough and flexible at extremely lowtemperatures, thus permitting their use in electrical circuitry such asthat employed in high speed switching circuits and super-conductorunits. Experiments conducted at temperatures of liquid helium (270 C.)have established that those polymers are quite resistant to breakage onflexing and that the substrate surface such as a metal foil backingmember is more susceptible to fracture than is the polymer.

Poly-p-xylylenes are obtained by the condensation of a polymer-formingvapor comprised of vaporous diradicals having the general structure YI'YYY (I! also more fully described hereinafter. Void-free coatings ofp-xylylene polymers have been prepared in this manner in thicknesses ofabout 100 A. units or greater.

Heretofore, vapor deposition of p-xylylene polymers has been limited tobatch coating of relatively small substrates such as sheetlike, flexibleor rigid materials of paper, plastic, glass, metal, fabrics or othersimilar materials. Preparation of unsupported p-xylylene films hassimilarly been limited to vapor casting onto a substrate and subsequentbatch-wise removal by stripping. These batch-wise methods have severelylimited the scope of application and commercial usefulness of thep-xylylene polymer family.

The primary difficulty which has severely hindered the development of acontinuous p-xylylene polymeric coating operation arises from theinability which has heretofore existed in providing satisfactory meansfor confining the diradical vapors during the coating operation. Thesevapors, under the pressures employed, behave as a highly randomlydiffusive gas which penetrates minute openings and, upon contact withcool surfaces, polymerizes thereon as a tough, horny deposit whichinterferes with the substrate handling means such as the supportingsurfaces, rollers, bearings, and other mechanical parts and soon rendersthem inoperative by restraining movement of said parts. These extraneousdeposits on the handling means can also damage fragile, low tensilesubstrates such as thin aluminum foils, paper and other thinly coatedproducts by scratching, abrading or tearing such products.

Application of known methods for confining vaporous substances haveproven unsatisfactory. Mainly, these methods pertain to vaporized metalsor gases which do not have the diffusive flow properties of the vaporscontaining p-xylylene diradicals or the characteristics of the polymericp-xylylene deposits at the pressures conventionally employed in thesemethods. Low pressure metal vaporization or gas formation techniquesresult in purely a physical phase change resulting in molecularstraightline flow which is relatively simple to contain. Most priormethods depend on passage of the substrate through gradient pressurestages. Multiple pressure graded stages such as differentially pumpedvacuum chambers are connected by seals through which the substrate orcoated material pass. These seals are restricted passages typicallyconsisting of contacting resilient material or close clearance orifices.These seals are designed to minimize external air or gas inleakage.Where, however, thin, yet continuous, depositions are required, theserestricted designs are severely limiting because of the possibility ofdamage to the delicate substrates by abrading, scratching or tearing.

Accordingly, it is an object of the present invention to provide amethod and apparatus for continuously or semi-continuously coatingsubstrate surfaces of various cross sectional profiles with apolymer-forming vapor.

It is another object of the present invention to provide a method andapparatus for continuously or semi-continuously coating substratesurfaces with extremely thin, yet continuous, coatings Without damage tosuch delicate substrates as was caused by prior existing methods whichdepend on passage of such substrates through close clearance orifices.

It is still another object of the present invention to provide means forconfining highly diffusive vapors and for preventing their condensationand polymerization on substrate handling means.

It is a still further object of the present invention to provide amethod and apparatus for continuously or semicontinuously formingunsupported p-xylylene polymeric films.

These and other objects are accomplished by the present invention oneaspect of which provides an apparatus for coating substrate surfaceswith a polymer-forming vapor which comprises a vapor deposition chamber,means for creating and maintaining a vacuum in said chamber, a generatoradapted to provide and distribute within said chamber a highly diffusivestream of a polymer-forming vapor, substrate handling means freelycommunicating with said deposition chamber and adapted to provide atleast one pass of the substrate surfaces therethrough, and a housingsurrounding said deposition chamber and substrate handling means adaptedto provide a pressure envelope about said chamber sufiicient to confinethe vaporous stream thereto.

Another aspect of the present invention provides a method for coatingsubstrate surfaces with a polymerforming vapor which comprises feeding asubstrate surface from a first zone of reduced presure into a closeclearance vapor deposition zone, contacting the substrate surface uponat least one pass of said substrate surface through the deposition zonewith the polymer-forming vapor and condensing said vapor thereon to forma continuous polymeric film, said first zone encompassing saiddeposition zone and freely communicating therewith, said first zoneadapted to be maintained at a higher pressure relative to saiddeposition zone to confine the polymerforming vapors thereto, andthereafter returning the coated substrate to said first zone.

FIGURE 1 is a schematic representation, partially in section, of anembodiment of the coating apparatus of the present inventionparticularly suitable for single pass coating of a substrate;

FIGURE 2 is a schematic representation, partially in section, of anotherembodiment of the coating apparatus particularly suitable for multi-passoperations;

FIGURE 3 is a schematic representation, partially in section, of anotherembodiment of the coating apparatus of the present invention whichprovides for continuous formation of an unsupported vapor-depositedfilm;

FIGURE 4 is a schematic illustration of another embodiment of thecoating apparatus which employs two skewed rolls enabling a large numberof passes, e.g., up to about 16, or more, per unit without acommensurate increase in the number of rolls needed for substratehandling;

FIGURE 5 is a schematic plan view of the skewed rolls shown in FIGURE 4;

FIGURE 6 is a schematic representation, partially in section,illustrating the use of a barometric leg seal which permits passage ofthe substrate through wide pressure differentials without allowingatmospheric in-leakage. Moreover, this embodiment permits continuousfeeding and removal of substrates to and from the deposition chamberfrom and to the atmosphere.

Referring now to FIGURE 1, there is shown an embodiment of the coatingapparatus of the present invention adapted to provide a single pass ofthe substrate through the deposition chamber. Deposition chamber 10 hasan inlet 12 and outlet 14 therein to allow free passage therethrough ofa substrate 16 to be coated. A vacuum is created and maintained withinsaid deposition chamber 10 by means of vacuum ports 18 and 20 externallycon nected to vacuum pumps (not shown). These vacuum ports are ofsufficiently large volume and so spaced with respect to the depositionchamber 10 so as to provide effective removal of excess vapor and propermaintenance of vacuum conditions. The Walls of the deposition chamber 10in the immediate vicinity of the vacuum ports 18 and 20 are preferablyenlarged to reduce the velocity of the vapors in those areas permittingmore effective vapor removal. A generator 22 is adapted to provide anddistribute through distribution nozzle 24 a stream of polymer-formingvapor to said chamber 10. Substrate handling means such as substratesupply roll 26 and windup roll 28 for the coated product along withappropriate guide rolls such as rolls 30 and 32 are adapted to provide asingle pass of the substrate 16 through the deposition chamber 10. Ahousing 34 surrounds both the deposition chamber 10 and the substratehandling means such as rolls 26, 28, 30 and 32 and isadapted to providea pressure envelope 36 about said chamber 10 which cooperates with theinlet 12 and outlet 14 of said chamber 10 to confine the stream ofpolymer-forming vapor within the deposition chamber 10. This can beaccomplished by maintaining a higher pressure in said envelope relativeto the pressure within the deposition chamber or by maintaining a lowerpressure in said envelope relative to said chamber pressure. In thelatter instance, however, it is considered critical that the capacity ofthe vacuum pumps be sufiicient to provide complete removal of excessvapors.

In actual operation, the pressure within the deposition chamber 10' isreduced to from about 1.0 micron to about 25 mm. Hg as more fullydescribed hereinafter by means of vacuum ports 18 and 20. A suitableprecursor of the polymer-forming vapor is pyrolyzed in generator 22. Thevaporous stream thus formed is passed through distribution nozzle 24into the deposition chamber 10 and there deposits on the substrate 16passing through said chamber 10. The deposition chamber 10 is preferablyencompassed by a relative higher pressure envelope 36 contained withinhousing 34. Housing 34 is a substantially airtight chamber of suitablesize and shape to accommodate both the deposition chamber 10 andsubstrate handling means such as substrate supply roll 26, transporthandling facilities such as rollers 30 and 32 for tensioning,supporting, cooling and guiding, as well as coated substrate Wind-uproll 28. Also, there can be included in said housing 34 means (notshown) for pressure measurement, chamber access, driving means forsubstrate supply and windup, and the like.

Deposition chamber 10 provides maximum deposition rate and efiiciency byemploying close clearances between the substrate 16 and walls of thedeposition chamber 10 thereby providing maximum system pressure whichprovides maximum collisions of the vaporous diradicals with thesubstrate surfaces. Although readily apparent, the dimensions of thedepositions chamber are commensurate with practical regard to thebehavior of the coated substrate, e.g., warpage or edge curlingtendencies of some substrates or Webs such as aluminum foil, and alsothe degree of polymer build-up on the chamber walls although this can beminimized by heating said chamber walls. It has been found that aminimum clearance of at least about g-ll'lcl'l is suflicient in mostinstances to provide free passage of the substrate through thedeposition chamber without damaging the substrate or coated product.Preferably however, the clearance between the substrate and the innerwalls of the deposition chamber are from about -inch to about 2 inches.Greater clearances can be employed; however, there is a substantialreduction in deposition efi'iciency as the clearance is increased muchabove 2 inches. The length of the deposition chamber 10 can varydepending upon the required residence time needed to obtain thethickness of coating desired and also practical handling limitationsimposed by the substrate. For example, with thin metallic foilsubstrates such as aluminum foil, distances over which the foil isunsupported are kept to a minimum in order to attain proper flatness ofthe substrate. In such instances the length of the deposition chamber 10which is substantially the length of the unsupported span is less thanabout 4 feet although a longer or shorter deposition chamber can beemployed with appropriate modifications readily apparent to thoseskilled in the mechanical arts. The linear speed of the substratethrough the deposition chamber can be varied to obtain the desiredcoating thickness; however, it is preferably from about 1 inch perminute to about 500 feet per minute.

The deposition chamber 10 is provided with vacuum ports 18 and 20respectively which are of sufficiently large volume and are so situatedwith respect to the deposition chamber proper and the inlet 12 andoutlet 14 thereto as to provide for effective vapor removal. Externalcold traps (not shown) are preferably attached in the vacuum lines. Useof such cold traps in the vacuum lines has been found to aid in theremoval of an appreciable amount of the condensable excess vapors,thereby increasing pumping efiiciency and minimizing cleaningrequirements of the vacuum lines.

Where space or other considerations do not permit vacuum ports which areof adequate size to provide substantially complete removal of the excessdiradical vapors, it is preferred to have the envelope 36 between thedeposition chamber and the housing 34 at a relatively higher pressurealthough still sub-atmospheric, than that which exists within thedeposition chamber 16 in order to assure no migration or leakage ofdiradical vapors into envelope 36 thereby preventing deposition on thesubstrate handling means situated in said envelope 36. Inert gases suchas nitrogen, argon and the like can be injected through nozzle 38 in thehousing 34 which provides communication of an external inert gas supply(not shown) with the envelope 36. This means of increasing the envelopepressure is also available when it is desired to increase the totalsystem pressure for increased deposition rate.

Polymer-forming vapors formed in generator 22 enter the depositionchamber 10 through distribution nozzle 24 either transverse to thelongitudinal axis of the substrate 16 as shown in FIGURE 1 or normal tothe substrate surface as shown in FIGURE 4. The distribution nozzle 24is preferably situated in the middle of the deposition chamber 10thereby providing equidistribution of the vapors along the substratelength as well as facilitating confinement of the excess vapors.

The vapors containing the p-xylylene diradicals can I be formed byeither of several techniques. The method found most convenient andpreferred is by the pyrolysis at temperatures between 450 C. and 700 C.of at least one cyclic dimer represented generally by the structure Y YI I YzTQ-TYz wherein Y is any monovalent inert substituent group,preferably hydrogen, although on the aromatic nucleus, it can be anyinert substituent group when starting with this dimer. On pyrolysis, thedimer cleaves into two separate reactive vaporous diradicals each havingthe structure .YzC C Y2.

I I Y Y where R is a lower hydrocarbon group, and Y is any non-polarsubstituent. These sulfones pyrolyze on heat- 6 ing to temperatures ofabout 600-l000 C. into sulfur dioxide and the reactive diradical I I Y Ywherein Y is a non-polar substituent. These sulfones pyrolyze on heatingto temperatures of about 400800 C. into sulfur dioxide and 2 moles ofmonoradical of the formula which disproportionates into a p-Xylene and adiradical of the structure l Y Y as is disclosed in copendingapplication Ser. No. 232,247 entitled, Diarylsulfones and Process forthe Pyrolysis Thereof to the Corresponding Diarylethanes and Polymers,filed Oct. 22, 1962, which is herewith included by reference.

Any other technique of making the vaporous diradicals can of course beused. Since some of these techniques produce other gaseous by-products(such as $0 and since certain of the metallic substrates employed may besubjected to attack by such lay-products, care should obviously be usedin selecting the metallic substrate when employing such reactivediradicals. Since the pyrolysis of the cyclic dimer di-p-xylyleneinvolves no other byproducts and the dimer cleaves quantitatively intotwo moles of the reactive diradical, this method is most preferred.

Inasmuch as the coupling and polymerization of these reactive diradicalsupon the condensation of the diradicals does not involve the aromaticring, any unsubstituted or desired substituted p-xylylene polymer can beprepared since the substituent groups function essentially as an inertgroup. Thus, the substitutent group can be any organic or inorganicgroup which can normally be substituted on an aromatic nuclei or on thealiphatic a-carbon atoms of such a diradical.

Notable among the monovalent inert groups that have been placed on thearomatic nuclei or aliphatic tat-carbon atoms of such poly(p-xylylenes)other than hydrogen are the halogens including chlorine, bromine, iodineand fluorine, alkyl groups such as methyl, ethyl, propyl, butyl andhexyl, cyano, phenyl, amino, nitro, carboxyl, benzyl and other similargroups. While some of the above groups are potentially reactive incertain conditions or with certain reactive materials, they areunreactive under the conditions of the present invention and hence aretruly inert in the instant case.

The substituted di-p-xylylenes and the aryl sulfones from which thesereactive diradicals are prepared, can be prepared by well knowntechniques. For example, the cyclic dimer, di-p-xylylene, is readilysusceptible to halogenation, alkylation and/ or oxidation and reductiontechniques and like methods of introduction of such substituent groupsinto aromatic nuclei. Inasmuch as the cyclic dimer is a very stableproduct up to temperatures of about 400 C., elevated temperaturereactions can also be employed for the preparation of varioussubstituted materials. When used herein, the term di-p-xylylene refersto any substituted or unsubstituted cyclic di-pxylylene as hereinabovediscussed, and the term pxylylene diradica refers to any substituted orunsubstituted p-xylene structure having a free radical on each of thealpha carbon atoms as hereinabove discussed.

In the polymerization process, the vaporous diradicals condense andpolymerize nearly instantaneously at the condensation temperature of thediradicals. The coupling of these diradicals involves such lowactivation energy and the chain propagation shows little or nopreference as to the particular diradical, so that stearic andelectronic effects are not important as they are in vinylpolymerization. The substituted and/ or unsubstituted p-xylylenehomopolymers can be made by cooling the vaporous diradical down to anytemperature below the condensation temperature of the diradical. It hasbeen observed that for each diradical species, there is a definiteceiling condensation temperature above which the diradical essentiallywill not condense and polymerize. All observed ceilings of substitutedp-xylylene diradicals have been below about 200 C. but vary to somedegree upon the operating pressure involved. For example, at 0.5 mm. Hgpressure, typical condensation and polymerization temperatures ob servedfor the following diradicals are:

C. p-Xylylene to Chloro-p-xylylene 70 to 80 n-Butyl-p-xylylene 130 to140 Iodo-p-xylylene 180 to 200 Dichloro-p-xylylene 200 to 250 ager,a-tetrafluoro-p-xylylene to Thus, by this process, homopolymer filmsare made by maintaining the substrate surface at a temperature below theceiling condensation temperature of the particular diradical specieinvolved, or desired in the homopolymer. This is most appropriatelytermed homopolymerizing conditions.

Where several different diradicals existing in the pyrolyzed mixturehave different vapor pressure and condensation characteristics, as forexample, p-xylylene and chloro-p-xylylene and dichloro-p-xylylene or anyother mixture with other substituted diradicals, homopolymerization willresult when the condensation and polymerization temperature is selectedto be at or below that temperature where only one of the diradicalscondense and polymerize. Thus, for purposes within this application, theterms under homopolymerization conditions are intended to include thoseconditions where only homopolymers are formed. Therefore it is possibleto deposit homopolymers from a mixture containing one or more of thesubstituted diradicals when any other diradicals present have differentcondensation or vapor pressure characteristics, and wherein only onediradical specie is condensed and polymerized on the substrate surface.Of course, other diradical species not condensed on the substratesurface can be drawn through the vacuum ports of the apparatus ashereinabove described, in vaporous form to be condensed and polymerizedin a subsequent cold trap.

Inasmuch as unsubstituted p-xylylene diradicals, for example, arecondensed at temperatures about 25 to 30 C., which is much lower thandichloro-p-xylylene diradicals, i.e., about 200 to 250 C. it is possibleto have present such diradicals in the vapor pyrolyzed mixture alongwith the dichloro-substituted diradicals. In such a case,homopolymerizing conditions are secured by maintaining the substratesurface at a temperature below the ceiling condensation temperature ofthe substituted pxylylene but above that of the p-xylylene, thuspermitting the p-xylylene vapors to pass through the vapor ports of theapparatus without condensing and polymerizing but collecting thepoly-p-xylylene in a subsequent cold trap.

It is also possible to obtain substituted copolymers through thepyrolysis process hereinabove described. Copolymers of p-xylylene andsubstituted p-xylylene diradicals, as well as copolymers of differentsubstituted p-xylylene diradicals wherein the substituted groups are allthe same but each diradical containing a differing number of substituentgroups can all be obtained through said pyrolysis process.

Copolymerization occurs simultaneously with condensation upon cooling ofthe vaporous mixture of reactive diradicals to a temperature below 200C. under copolymerization conditions.

Copolymers can be made maintaining the substrate surface at atemperature below the ceiling condensation temperature of the lowestboiling diradical desired in the copolymer, such as at room temperatureor below. This is considered copolyrnerizing conditions, since at leasttwo of the diradicals will condense and copolyrnerize in a randomcopolymer at such temperature.

In the pyrolytic process of a di-p-xylylene the reactive diradicals areprepared by pyrolyzing the substituted and/ or unsubstituteddi-para-xylylene at a temperature between about 450 C. and about 700 C.,and preferably at a temperature between about 550 C. to about 600 C. Atsuch temperatures, essentially quantitative yields of the reactivediradical are secured. Pyrolysis of the starting di-p-Xylylene begins atabout 450550 C. but such temperatures serve only to increase time ofreaction and lessen the yield of polymer secured. At temperatures aboveabout 700 C., cleavage of the substituent group can occur, resulting ina tri-/or polyfunctional species causing cross-linking and highlybranched polymers.

Pyrolysis temperature is essentially independent of the operatingpressure. For most operations, pressures within the range of 1.0 micronto 25 mm. Hg are most practical for pyrolysis. Likewise if desirable,inert vaporous diluents such as nitrogen, argon, carbon dioxide, heliumand the like can be employed to vary the optimum temperature ofoperation or to change the total effective pressure in the system.

Various modifications of the apparatus shown in FIG- URE 1 can beconveniently made to increase productivity. For example, multiplesuccessive coating treatments can be obtained by passing the substratethrough a series of deposition chambers of the type shown in FIGURE 1all contained within a common housing. Suitable guide and cooling rollssituated in the common outer envelope can provide communication betweensuccessive deposition chambers.

A preferred embodiment shown in FIGURE 2 provides series multiplepassage of the substrate through the deposition chamber with interstagepasses being supported and cooled in the outer envelope. The apparatusshown in FIGURE 2 is similar to that shown in FIGURE 1 except that thesubstrate handling means have been modifi'ed to provide a seriesmultipass system. Rollers 29, 30 and 31 provide multiple passage of thesubstrate 16 through the deposition chamber 10 and are adapted to beinternally cooled thereby lowering the surface temperature of thesubstrate and increasing the deposition rate of the p-xylylenediradicals thereon. Rollers 32, 33 and 35 are appropriate tensioningidlers and guide rolls. This embodiment provides a highly compact andeconomic coating apparatus.

FIGURE 3 shows another embodiment of the present invention which permitsunsupported poly-p-xylylene films to be continuously formed by beingvapor cast onto a cooled, continuously moving carrier surface such as abelt or drum, continuously stripped therefrom and thereafter passed towind-up in the outer envelope. By this method, it is possible to obtaincontinuous lengths of poly-p-xylylene film of extremely thin crosssection. As shown in FIGURE 3, an endless cooled surface such as arotating drum 19 continuously rotates within the depsition chamber 10.p-Xylylene diradicals formed by pyrolysis in generator 22 as describedabove are passed into the deposition chamber 10 through distributionnozzle 24 and there condense and polymerize on the cool surface of therotating drum 19. The poly-p-xylene film 17 thus formed is stripped fromthe drum 19 and passed through an outlet 14 in the deposition chamber 10to wind-up on roll 28. The apparatus can also be easily modified topermit coating of substrate surfaces and simultaneous temperaturecontrol of the substrate by contact with the drum surface. The substrate16 (shown dotted) can be fed from appropriate substrate handling means(shown dotted) to the deposition chamber 10 through an inlet 12 therein.'The coated product can be removed as above described and, if desired,the coated substrate can undergo a post-stripping operation to providecontinuous unsupported film.

FIGURE 4 illustrates a modification of the apparatus of the presentinvention which enables multiple passes, for example, up to 16 passes ormore, through the deposition chamber while using only two driven, cooledmain process rolls. This embodiment has been found to effect veryuniform diradical vapor distribution resulting in improved productuniformity. As shown in FIGURE 4, the substrate 16 is fed to a roll 40situated in the outer envelope 36 between the housing 34 and the dualdeposition chambers 11 and '13. The substrate 16 passes throughdeposition chamber 11 equipped with vacuum ports 42 and 44 and passesbetween the split distribution nozzle 25 whereby the substrate surfacesare coated by condensing diradical vapors which impinge perpendicularlyon both surfaces thereof. The coated substrate is then passed to roll 46whose axis is skewed in relation to the axis of roll 40. The coatedsubstrate thereafter passes through the second deposition chamber 113equipped with vacuum ports 43 and 45 where it is additionally coatedupon passage through split distribution nozzle 27 and is then returnedto roll 40. Due to the cross-axis or skewed axis main process rolls, thesubstrate is made to follow a spiral path as it passes over the rollsand can therefore be easily made to undergo multiple passes of the typedescribed above; the number of said passes depending solely on the sizeof the rollers and the amount of coating desired on a particularsubstrate as dictated by end-use considerations. The use of splitdistribution nozzles 25 and 27 enables the diradical vapors emanatingfrom generator 22 to impinge perpendicularly on the substrate surfaceson successive passes through the split distribution nozzles 25 and 27thereby improving uniformity of deposition across the width of thesubstrate substantially eliminating any problems of non-uniform coatingwhich can arise in transverse coating.

FIGURE is a plan view of the skewed axis rolls of FIGURE 4 illustratingthe relationship of the roll axes. It is considered preferable that theaxis of the bottom roll 40 be perpendicular to the back wall of thehousing whereas the axis of the top roll 46 be skewed relative to theaxis of the bottom roll 40; however, it is critical that the skewedroll, whether it be the top or bottom roll have its axis ofiset so thatthe sum of the offset distances shown as X and Y is at least equal toand preferably greater than the width of the substrate to be coated. Itis considered desirable that the central axis of both rolls cross at thelongitudinal midpoint of each axis when viewed vertically as shown.

It is often desirable, especially in continuous coating operations, tofeed the substrate and/or wind-up the coated product under normalatmospheric conditions. Due to the need for vacuum conditions in theprocess, however, a Wide pressure differential must be overcome to allowfeed or wind-up under normal conditions. It has been found that thistransfer can be conveniently accomplished by passing the substrate fromthe atmosphere through a barometric leg seal into the deposition chamberwherein the p-xylylene film-forming composition is continuouslydeposited on the substrate which is then returned to the atmospherethrough another barometric leg seal and passed to wind-up. FIGURE 6 is apartial schematic illustration, partly in section, of such anatmosphere-vacuum-atmosphere transfer system. For simplicity, only thatportion of the apparatus relating to the removal of the coated substratefrom the deposition chamber to the atmosphere is shown. The reversesituation of feeding a substrate supply into the deposition chamber isreadily "apparent to those skilled in the art. The housing 34 shown inFIGURES 1-3 is modified to housing 35 of FIGURE 6 by removing wind-uproll 28 from within the envelope 36 and replacing it with guide roller39 and attaching barometric leg 48. Barometric leg 48 is a substantiallyair tight I-shaped housing containing a liquid metal sealant 50 andguide roller 52 for the coated product. The roller 52 and externalroller 54 support the coated product passing from the sub-atmosphericenvelope 36 in transit through the leg 48 to the atmosphere and wind-upon roll 28. Drain -56 controlled by valve 58 is provided in order todrain the liquid sealant 50 for convenience in threading the substrate16 through the roll system for start-up.

Liquid metals such as mercury or low melting alloys such as Woods metalare considered preferable for use as the liquid sealant due to thenominal size leg required as opposed to a 34 foot leg for water or oil.Moreover, the use of such liquid metals or low melting alloyssubstantially preclude the problem of contamination or carry-over due towetting. Due to the possibility of alloying with mercury of someunprotected substrates, it may not always be desirable to employ amercury barometric leg for introducing such substrates into the vacuumdeposition chambers. Substrates coated with a film of a poly-p-xylylene,however, are completely resistant to attack or permeation by mercury orother liquid metals and are therefore readily amenable to wind-upthrough a mercury barometric leg seal.

The following examples are for illustrative purposes only and are not tobe construed as imposing any limitations on the present invention.

EXAMPLE I Employing the apparatus shown in FIGURE 1, dead soft aluminumfoil 1 inch in width and 0.00025-inch gauge thickness was passed throughthe deposition chamber maintaining a clearance of -inch with thedeposition chamber walls and was coated on both surfaces thereof with apoly-p-xylylene film. An external cold trap was employed as well as a 13cubic feet/min. mechanical rotary vacuum pump system having an estimatedeffective capacity for noncondensables at 6-8 cubic feet/min. whichdeveloped an absolute pressure of about 0.8 and 0.4 mm. Hg in the outerenvelope and deposition chamber, respectively, when nitrogen at cc./min. STP was bled into the outer envelope. The nitrogen bleed raised thetotal system pressure thereby promoting high deposition rates. The inertgas flow also aided in developing a pressure gradient from the envelopeinto the end openings of the deposition chamber which effectively sweptback the excess diradical vapors. During operation, pressure at thedeposition chamber outlet rose to about 0.45-0.60 mm. Hg. The p-xylylenediradicals were generated by subliming cyclic di-p-xylylene at anaverage dimer sublimation rate of about 0.5 grams/minute in a quartzsublimation chamber connected to a quartz pyrolysis tube.

The cyclic dimer was sublimed at a temperature of about 125 -250 C. anda pressure of 0.11 mm. Hg absolute. The vapors were passed to thepyrolysis zone maintained at temperatures between about 6S0-'700 C.thereby forming the reactive p-xylylene diradicals which were fedthrough a distribtuion nozzle into the deposition chamber and therecondensed on the cool substrate surfaces passing therethrough. Thesubstrate was cooled by passage over cooling rolls in the outerenvelope. The rolls were cooled by recirculating temperature controlledmethanol at 20 C. within said rolls. The polymer, poly-p-xylylene wasdeposited as a transparent, flexible, tough coating on each face and theedges of the aluminum foil as it passed through the deposition chamber.Polymeric deposits on the deposition chamber walls was not consideredobjectionable. There was no evidence of diradical vapors enter ing theouter envelope.

Several runs were made in the above manner varying only the linear speedof the unsupported aluminum foil web through the deposition chamber. Itwas found that the average coating thickness varied with the linearspeed as follows:

Coating thickness Linear web speed (microns) (feet/ min.) 0.8 1.4 1.10.8 2.6 0.4

EXAMPLE H between about 0.05-0.07 inch. An external cold trap wasemployed as well as a 24 c.f.m. mechanical vacuum pump system having anestimated effective capacity of noncondensables at 1012 c.f.m. whichdeveloped an absolute pressure of about 0.34 and 0.27 mm. Hg in theouter envelope and deposition chamber, respectively, when nitrogen wasbled into the outer envelope at 80 cc./min. STP. Pressure at thedeposition chamber outlet rose during operation to about 0.300.40 mm.l-lg. The p-xylylene diradicals were produced as described in Example Iwith an average dimer sublimation rate of about 0.23 grams/minute. Thesurface of the aluminum foil webs were cooled between passes through thedeposition chamber by passage over cooling rolls in the outer envelope.The rolls were cooled by recirculating temperature controlled methanolat '20 C. within said rolls. The linear speed of the aluminum foil webthrough the deposition chamber was about 0.9 ft./min. with a resultinguniform coating of poly-p-xylylene thereon having a thickness of about1.6 microns per side. Deposits on the deposition chamber walls were notconsidered objectionable. There was no evidence of diradical vaporsentering the outer envelope.

Although the present invention has been described mainly in reference tocoating of substrate surfaces with films of poly-p-xylylenes, it isreadily apparent that various modifications of the apparatus or coatingprocess can be made to accomplish other objectives. For example,pretreatment of the substrate or interim pass treatments of the partialor completely coated substrate can be made, such as vacuum metallizing,sputtering, ionic bombardment for cleaning or processing, orcodeposition with metallic and/or other organics from the vapor phase oras alternate deposits therewith. In these embodiments, modifieddeposition chambers of the present invention or those of known designfor accomplishing such treatments can be employed within a commonhousing. Thus, the substrate can undergo a series of varying treatmentsupon passage through a series of deposition or treatment chambers withsuitable guide and cooling rolls interposed between the chambers in thecommon outer envelope, Em-

ploying the higher pressure envelope of the present invention, largerclearance seals at the inlet and outlets to these chambers can be usedthereby eliminating any possibility of damage to fragile substrates dueto material build-up at these points. As described hereinabove, vaporshaving highly diffusive tendencies, such as those vapors containingp-xylylene diradicals, are confined to the deposition chamber therebyeliminating any fear of harmful deposits on the substrate handling meansin the outer envelope deposite the use of larger inlets and outlets tothe deposition chamber.

Further modifications of the apparatus of the present invention can bemade to provide means of regulating the areas to be coated. Coating onlyone side of a substrate is often desirable in order to obtain highcoating productivity, economy, and/ or maximum product quality byselective use of the best surface of the substrate. In coating aluminumfoil for use as capacitors, for example, it is desirable to coat onlythe best side, i.e., the smooth or bright side, for peak electricalfunctionality. One-surface coating of substrates can easily beaccomplished in the present invention by running two substrates back toback, i.e., in close contact with each other and with their respectivebright surfaces exposed, through the deposition chamber at the samelinear speed or preferably at differential speeds, and subsequentlyseparating the 'substrates by wind-up on separate rolls. This could alsobe accomplished by employing an expendable, dummy web moving through thedeposition chamber in close contact with the substrate-the substratehaving its bright surface exposed.

Still a further modification can be employed to provide not only singlesurface coating but also a substantial increase in coating capacity bycontinuously cooling the substrate during passage through the depositionzone. This is conveniently accomplished by providing a stationarysintered or porous stage which extends through the deposition chamberand is coextensive with the path the substrate will follow through thedeposition chamber. The porous stage is adapted to admit a slight bleedof a cool inert gas through the pores thereof into the depositionchamber. This inert gas bleed both cools and cushions the substrate,simultaneously sweeping the diradical vapors away from the underside ofsaid substrate and thus permitting only one surface of the sub strate tobe coated.

Due to the extremely thin coatings provided by the present invention,the substrates so coated are useful in miniaturized or microminiaturizedelectric circuitry, for example, a metallic foil or wire substrate canbe completely coated with a thin film of a poly(p-xylylene) andsubsequently with a conductive metal vapor deposited film. The thusformed laminate can then be used as a planar capacitor or it can beWound in the conventional manner and used as a rolled capacitor.

Since certain changes can be made in the above method and apparatuswithout departing from the scope of the invention herein described, itis intended that all matter contained in the above description or shownin the accompanying drawing shall be interpreted as ilustrative and notin a limiting sense.

Although the present invention has been described with particularreference to the vapor deposition of continuous films of p-xylylenepolymers, it is also considered as within the scope and spirit of thepresent invention that the method and apparatus herein described isequally applicable to other polymer-forming compositions which can bevapor deposited or, being polymers initially, can be transferred in thevapor state and subsequently deposited as a continuous film.

What is claimed is:

1. Apparatus for coating substrate surfaces with a film-formingcomposition which comprises a deposition chamber, having an open inletand outlet, a generator adapted to provide and distribute within saidchamber a highly diffusive vaporous stream of a film-formingcomposition, substrate handling means freely communicating with saiddeposition chamber adapted to provide at least one pass of the substratesurfaces therethrough, a housing surrounding said deposition chamber andsubstrate handling means, said housing adapted to maintain a pressureenvelope about said chamber and means for drawing a vacuum positionedwithin said chamber and proximately spaced from the inlet and outletthereof, said vacuum drawing means of sufficient capacity to create agaseous seal to confine the vaporous stream to said deposition chamber.

2. Apparatus for coating substrate surfaces with a film-formingcomposition which comprises a deposition chamber, a generator adapted toprovide and distribute within said chamber a highly diffusive vaporousstream of a film-forming composition, substrate handling means freelycommunicating with said deposition chamber and adapted to providemultiple passes of the substrate surfaces through said chamber, ahousing surrounding said deposition chamber and substrate handlingmeans, said housing adapted to provide a pressure envelope about saidchamber, and means to confine the film-forming vapors to the depositionchamber comprising vacuum ports having a capacity commensurate with andpositioned within said chamber and proximately spaced from the inlet andoutlet thereof to provide effective removal of the excess film-formingcomposition, thereby creating a gaseous seal.

3. Apparatus for coating substrate surfaces with a film-formingcomposition which comprises a deposition chamber, having an inlet andoutlet therein allowing unrestricted passage of said substrate throughthe deposition chamber while maintaining a close clearance between thesubstrate and the inner walls of the deposi tion chamber to providemaximum deposition rate, a generator adapted to provide and equallydistribute within said chamber a highly diffusive stream of afilmforming composition, substrate handling means adapted to cool thesubstrate and provide at least one pass of the cooled substrate surfacesthrough the deposition chamber, and a housing surrounding saiddeposition chamber and substrate handling means, said housing adapted toprovide a pressure about said chamber and means for drawing a vacuum offrom about 1 micron to about mm. Hg in said chamber comprising vacuumports having a capacity commensurate with and positioned within saidchamber and proximately spaced from the inlet and outlet thereof toprovide effective removal of the excess film-forming composition,thereby creating a gaseous seal to confine the film-forming vapors tothe deposition chamber.

4. Apparatus for coating substrate surfaces with a filmformingcomposition as defined in claim 3 wherein a clearance of from about toabout 2 inches is maintained between the substrate and the inner wallsof the deposition chamber.

5. Apparatus for coating substrate surfaces with a filmformingcomposition as defined in claim 3 wherein the housing has a nozzletherein adapted to inject an inert gas stream into the envelope betweensaid housing and the deposition chamber to increase the pressure in saidenvelope assuring no migration of vapors into said envelope andincreasing the deposition rate of the film-forming composition byincreasing the total system pressure.

6. Apparatus for coating substrate surfaces with a filmformingcomposition as defined in claim 3 wherein the housing surrounding saiddeposition chamber and substrate handling means has an outlet thereinadjacent the outlet to the deposition chamber to which is afiixed a J-shaped extension of said housing partially filled with a liquid metaland through which the coated substrate is passed from the envelope towind-up in the external atmosphere.

7. Apparatus for coating substrate surfaces with a film-formingcomposition which comprises a deposition chamber divided into twolaterally adjacent zones by at least one intervening wall, each zonehaving an inlet and outlet therein allowing unrestricted passage of saidsubstrate therethrough, a generatoradapted to provide and distribute toeach zone a highly diffusive stream of a film-forming composition whichimpinges on both surfaces of the substrate passing through each of saidZones, substrate handling means including two driven, cooled, mainprocess rolls situated outside the deposition chamber at the opposedextremities thereof, one of said rolls having its axis skewed inrelation to the axis of the other of said rolls causing the substrate tofollow a spiral path through the deposition chamber and enabling saidsubstrate to undergo multiple passes through each of said zones, ahousing surrounding said deposition chamber and substrate handling meansadapted to provide a pressure envelope about said chamber which freelycommunicates with the inlet and outlet of each of said laterallyadjacent zones, means for creating a drawing vacuum in each of saidzones comprising vacuum ports having a capacity commensurate with andpositioned within each of said zones and proximately spaced from theinlet and outlet of each of said zones to provide effective removal ofthe excess fi'mforming composition to create a gaseous seal to confinethe film-forming vapors to the deposition chamber.

8. Apparatus for coating substrate surfaces with a filmformingcomposition as defined in claim 7 wherein the axis of one of the twodriven, cooled main process rolls is skewed in relation to the axis ofthe other of said rolls so that, when viewed vertically, thelongitudinal axes of both rolls cross at the mid-point of each axis andthe sum of the distances by which the leading edge of one roll extendsbeyond the corresponding edge of the other roll plus the distance bywhich the laterally opposed edge of said one roll lags the correspondingedge of said other roll is at least equal to the width of the substrateto be coated.

9. Apparatus for coating substrate surfaces with a filmformingcomposition as defined in claim 8 wherein the housing surrounding saiddeposition chamber and substrate handling means has an outlet thereinadjacent the outlet to the deposition chamber to which is affixed a J-shaped extension of said housing partially filled with a liquid metaland through which the coated substrate is passed from the envelope towind-up in the external atmosphere.

10. Apparatus for forming a continuous film from a vapor depositedfilm-forming composition which comprises an endless, cooled, revolvingsurface, a deposition chamber having at least one aperture therein anddisposed about said cooled surface, a generator adapted to providewithin said chamber and to deposit on said cooled surface a highlydiffusive vaporous stream of a film-forming composition, stripping meansadapted to continuously strip the film formed on said cooled surface andfreely pass said stripped film to wind-up means through an aperture insaid deposition chamber, a housing surrounding said deposition chamberand stripping means adapted to provide a pressure envelope about saidchamber means for drawing a vacuum positioned within said chamber andproximately spaced from the aperture thereof, said vacuum drawing meansbeing of sufficient capacity to create a gaseous seal thereby confiningthe vaporous film-forming composition to the deposition chamber.

'11. Apparatus for forming a continuous film from a vapor-depositedfilm-forming composition which co-mprises an internally, cooled,rotatable drum, a deposition chamber having an inlet and outlet thereondisposed about said drum, substrate handling means freely communicatingwith said deposition chamber and adapted to provide passage of asubstrate surface therethrough, a generator adapted to provide withinsaid chamber and deposit on said substrate surface a highly diffusivevaporous stream of a film-forming composition, a housing surroundingsaid deposition chamber and substrate handling means adapted to providea pressure envelope about said chamber, means for drawing a vacuumpositioned within said chamber and proximately spaced from the inlet andoutlet thereof said vacuum drawing means being of sufficient capacity tocreate a gaseous seal thereby confining the vaporous film-formingcomposition to the deposition chamber.

12. Apparatus as defined in claim 11 wherein the substrate handlingmeans additionally includes means for stripping the vapor-deposited filmfrom the substrate surface to provide continuous unsupported film.

13. Apparatus for forming a continuous film from a vapor-depositedfilm-forming composition as defined in claim 11 wherein the housingsurrounding said deposition chamber and stripping means has an outlettherein adjacent to the outlet of the deposition chamber to which isaffixed a I-shaped extension of said housing partially filled with aliquid metal and through which the stripped film is passed from theenvelope to wind-up in the external atmosphere.

14. Method for coating substrate surfaces with a polymer-forming vaporwhich comprises feeding a substrate surface from a first zone of reducedpressure into a close clearance vapor deposition zone, contacting thesubstrate upon at least one pass of said substrate surface through thedeposition zone with the polymer-forming vapor and condensing said vaporthereon to form a continuous polymeric film of the condensed vapors,said first zone encompassing said deposition zone and freelycommunicating therewith, maintaining said first zone at a sufficientpressure relative to said deposition zone to create a differentialpressure gaseous seal to confine the polymer-forming vapor thereto, andthereafter returning the coated substrate to said first zone. 1

15. Method for coating substrate surfaces with a polymer-forming vaporwhich comprises continuously feeding a substrate surface from a firstzone of reduced pressure, wherein said substrate surface is cooled to atemperature below the condensation temperature of the polymerformingvapor, into a close clearance vapor deposition zone maintained at apressure of from about 1 micron to about millimeters Hg, contacting thecooled substrate surface upon at least one pass of said substratesurface through the deposition zone with the polymerforming vapor andcondensing said vapor thereon to form a continuous polymeric film of thecondensed vapors, said first zone encompassing said deposition zone andfreely communicating therewith, maintaining said first zone at asufiicient subatmospheric pressure relative to said deposition zone tocreate a differential pressure gaseous seal to confine thepolymer-forming vapor thereto, and thereafter returning the coatedsubstrate to said first zone.

16. Method for coating substrate surfaces with a polymer-forming vaporas defined in claim 15 wherein the linear speed of the substrate surfacepassing through the deposition zone is from about 1 inch per minute toabout 500 feet per minute.

17. Method for coating substrate surfaces with a polymer-forming vaporas defined in claim 15 wherein a close clearance of from about -inch toabout 2 inches is maintained between the substrate and the inner wallsof the deposition zone.

18. Method for coating substrate surfaces with a polymer-forming vaporas defined in claim 15 wherein an inert gas stream is injected into thefirst zone increasing the total system pressure and by freelycommunicating with the deposition zone, confining the polymer-formingvapor to said deposition zone.

19. Method for coating substrate surfaces with a polymer-forming vaporas defined in claim 15 wherein a cool, inert gas stream coextensive withthe path of the substrate through the deposition zone, cools thesubstrate and sweeps the polymer-forming vapor off one surface of saidsubstrate providing a substrate coated on only one surface thereof.

20. Method for coating substrate surfaces with a polymer-forming vaporas defined in claim 15 wherein the coated substrate upon re-entering thefirst zone is passed through a J shaped barometric seal partially filledwith a liquid metal to wind-up in the atmosphere.

21. Method for coating substrate surfaces with a filmforming compositionas defined in claim 15 wherein the polymer-forming vapor is comprised ofp-xylylene diradicals.

22. Method for coating substrate surfaces with a polymer-forming vaporwhich comprises continuously cooling a substrate surface to atemperature below the condensation temperature of the film-formingcomposition by passing said substrate over a first cooling means in asubatmospheric zone, passing said cooled substrate from saidsub-atmospheric zone into a first close clearance vapor deposition zone,feeding a stream of polymer-forming vapor to said first deposition zonewherein it impinges and condenses on said substrate passingtherethrough, imparting a spiral configuration to the path of the coatedsubstrate by passing said coated substrate over a second cooling meansin said subatmospheric zone, the axis of said second cooling means beingskewed relative to the axis of said first cooling means, reversing thedirection of the path of said coated substrate by passing over saidsecond skewed cooling means, passing said cooled coated substrate fromsaid subatmospheric zone into a second close clearance vapor depositionzone, feeding a stream of polymer-forming vapor to said seconddeposition zone wherein it impinges and condenses on said substratepassing therethrough, said subatmospheric zone encompassing both of saidfirst and second deposition zones and freely communicating therewith,said first and second deposition zones maintained at a pressure of fromabout 1 micron to about 25 mm. Hg, said subatrnospheric zone maintainedat a sufficient pressure relative to said deposition zones to create adifferential pressure gaseous seal to confine the polymer-forming vaporthereto, returning the thus coated substrate to said first cooling meansto complete at least one cycle and thereafter returning the coatedsubstrate to said subatmospheric zone.

23. Method for coating substrate surfaces with a polymer-forming vaporas defined in claim 22 wherein the linear speed of the substrate surfacepassing through the deposition zones is from about 1 inch per minute toabout 500 feet per minute.

24. Method for coating substrate surfaces with a polymer-forming vaporas defined in claim 22 wherein the coated substrate upon re-entering thesub-atmospheric zone is passed through a J-shaped barometric sealpartially filled with a liquid metal to wind-up in the atmosphere.

25. Method for coating substrate surfaces with a polymer-forming vaporas defined in claim 22 wherein the polymer-forming vapor is comprised ofp-xylylene diradicals.

26. Method for forming a continuous film from a polymer-forming vaporwhich comprises revolving an endless internally cooled surface within avapor deposition zone maintained at a pressure of from about 1 micron toabout 25 mm. Hg, feeding a stream of a polymer-forming vapor to saiddeposition zone which impinges and condenses on the cooled surfacerevolving therein, continuously stripping the film thus formed from therevolving surface, and thereafter passing said stripped film to wind-upin a sub-atmospheric zone encompassing said deposition zone and freelycommunicating therewith, said subatmospheric zone maintained at asufificient pressure relative to said deposition zone to create adifferential pressure gaseous seal to confine the vaporous streamthereto.

27. Method for forming a continuous film from a polymer-forming vapor asdefined in claim 26 wherein the stripped film is passed from thesub-atmospheric zone through a I-shaped barometric seal partially filledwith a liquid metal to wind-up in the atmosphere.

1 7 1 8 28. Method for forming a continuous film from a poly- 2,971,8622/1961 Baer et a1. 117-61 met-forming vapor as defined in claim 26wherein the 3,043,715 7/1962 Clough 117107 polymer-forming vapor iscomprised of p-xylylene di- 3,181,209 5/1965 Smith 118-49 radicals.3,301,707 1/1967 Loeb et al 117227 6 References Cited UNITED STATESPATENTS 2,879,739 3/1959 Bugbee et a1 118-49 H. MINTZ, AssistantExaminer.

ALEXANDER H. BRODMERKEL,

Primary Examiner.

